Blemish: A defect found on the surface of the pearl. Non-damaging blemishes include spots, bumps, pits and wrinkles, and can affect a pearl's price. Damaging blemishes -- which may worsen, and can affect the durability of a pearl as well as its price -- include cracks, holes and chips.

Button: A dome-shaped pearl with a flat bottom.

Choker: A pearl necklace that is 16 to 18 inches in length.

Circles: Concave, concentric rings on a pearl's surface.

Clean: Absence of blemishes on a pearl's surface.

Color: An evaluation of quality used to describe the color of a pearl.

Collar: A pearl necklace that is 10 to 13 inches in length.

Grafting: The insertion, through human intervention, of an irritant into the body or the mantle tissue of a mollusk, in order to produce a cultured pearl.

Lustre or Luster: The combination of surface shine and the depth of inner light refraction in a pearl. Lustre is one of the great determinants of a pearl's quality.

Mantle Tissue: The layer of thin tissue adhering a mollusk to its inner shell.

Matching: Using luster, surface, shape, color and size to match one pearl with another to create a piece of pearl jewelry, such as a necklace.

Matinee: A pearl necklace that is 20 to 24 inches in length.

Millimeter: The metric measurement used to determine the size of a pearl. One mm equals 1/25 of an inch.

Momme: The weight measurement for pearls in Japan. One momme equals 3.75 grams, or 18.7 carats.

Nacre: A calcium carbonate-based crystalline substance secreted by a mollusk as a defensive device against the intrusion of a foreign irritant into its body.

Nucleus: A small bit of polished shell from an American freshwater mollusk used as an irritant and inserted into the body of a saltwater mollusk. By the same token, a small bit of soft mantle tissue from one freshwater mussel is inserted as an irritant into the body of another freshwater mollusk.

Nucleation: Also called grafting or implementation, this is the process of inserting an irritating nucleus into the body of a mollusk so that it will secrete nacre to cover it, consequently producing a cultured pearl.

Opera: A pearl necklace that is 28 to 32 inches in length.

Princess: A pearl necklace that is 17 to 19 inches in length.

Rope: A pearl necklace over 45 inches in length.

Shape: A quality evaluation, describing the shape of a pearl. Round is the most prized shape in the industry, but saltwater and freshwater pearls are produced in a variety of shapes, just as they exhibit a variety of colors.

Size: The diameter of a pearl measured in millimeters and used as a quality and price evaluation of the pearl.

Sorting: Separating pearls by surface, shape, color and size prior to the jewelry matching process.

Surface: A quality evaluation of the amount of blemishes on a pearl, ranging from clean to heavily blemished.